WO2003104507A1

WO2003104507A1 - Hard metal substrate body and method for producing the same

Info

Publication number: WO2003104507A1
Application number: PCT/DE2003/001834
Authority: WO
Inventors: Dieter Kassel; Werner Daub; Klaus Dreyer; Klaus RÖDIGER; Walter Lengauer; Mariann Lovonyak; Vera Ucakar
Original assignee: Kennametal Widia Gmbh & Co. Kg
Priority date: 2002-06-10
Filing date: 2003-06-04
Publication date: 2003-12-18
Also published as: JP2005529236A; PT1511870E; DE50307024D1; EP1511870B1; ATE359381T1; US20050224958A1; DE10225521A1; EP1511870A1

Abstract

The invention relates to a hard metal substrate body consisting of a WC hard material phase and between 3 and 25 mass % of a binding phase containing at least one binding metal Fe, Co and/or Ni, and up to 15 mass % (in relation to the binding phase) of dissolved dopants from the group containing AI, Cr, Mo, Ti, Zr, Hf, V, Nb, Ta. The invention also relates to a method for producing one such hard metal substrate body, using powder metallurgy followed by sintering. According to the invention, the percentage of all of the dopants in the hard metal is limited to a maximum of 4 mass %, the proportion of cubic phase in the hard metal is less than 4 vol. %, and the binding metal content in an edge region of the hard metal substrate body falls from up to 1 μm, preferably up to 0.5 μm, to less than half the binding agent content inside the substrate body. In order to produce said hard metal substrate body, once the eutectic has been reached and at the latest once the sintering temperature has been reached in the heating phase, the vacuum or inert gas atmosphere is replaced by a N₂ atmosphere and maintained at least until the sintering temperature is reached.

Description

description

Tungsten carbide substrate body and method for its production

The invention relates to a hard metal substrate body consisting of a WC hard material phase and a 3 to 25 mass% binder phase which, in addition to at least one of the binder metals Fe, Co and / or Ni, also comprises up to 15 mass% (based on the binder phase). contains dissolved dopants from the group AI, Cr, Mo, Ti, Zr, Hf, V, Nb, Ta.

The invention further relates to a method of such a hard metal substrate body, in which the starting mixture is pretreated by powder metallurgy, pressed into a green body and finally heated and sintered in an atmosphere of a furnace.

In the hard metal compositions mentioned, the dopants, which are mostly added in the form of carbides, nitrides or carbonitrides of the elements Ti, Zr, Hf, V, Ta or alloys of these elements, in particular Ti ₂ AIN or Ti ₂ AIC, act as Grain growth inhibitors, which ensure that the WC-Co base alloy produced remains fine-grained and uniform in order to ensure optimum hardness and wear resistance.

It has also long been known that the wear properties of hard metal bodies can be influenced by applying one or more surface layers made of carbides, nitrides, carbonitrides, borides and / or oxides or diamond. Chemical or physical coating processes were mentioned early on, namely in DE-A 24 33 737 or DE-A-25 25 185.

DE 27 17 842 A1 states that in order to save the separate work step that is required for the application of layers by means of CVD or PVD It would make sense to expose the hard metal body to a pressure between 2 bar (2 x 10 ⁶ Pa) and 5000 bar (5 x 10 ⁸ Pa) under nitrogen-containing atmosphere after the final sintering at high temperatures. The treatment temperature should be between 800 ° C and an upper limit that is at least 50 ° C below the maximum sintering temperature. With this "surface embroidery", which should be effective to a depth of 300 μm, an improved wear behavior as well as an improved oxidation resistance and a lowering of the diffusion and sticking tendency of the hard metal during its interaction with the wear partner should be guaranteed. For many practical applications, however, a surface coating is still indispensable. The problem of poor adhesion of the coating on the substrate body arises in particular in the case of diamond coatings, but also coatings of a different composition. The cause of poor adhesion is, for example, too high a binder content on the substrate body surface.

DE 199 22 059 A1 describes a hard metal or cermet body with a hard material phase made of WC and / or at least one carbide, nitride, carbonitride and / or oxicarbonitride of at least one of the elements IVa, Va or Vla group of the periodic table and a binder metal phase made of Fe, Co and / or Ni, the proportion of which is 3 to 25% by mass, in which WC crystallites protrude from the body surface by 2 to 20 μm. This is to be achieved by either pressing a nitrogen-free mixture of hard materials and binding metals into a green body and heating it in a vacuum or inert gas atmosphere to a temperature between 1200 ° C and the sintering temperature, after which at the latest at

If the sintering temperature is reached, at least temporarily, a nitrogen and possibly carbon-containing atmosphere is set at a pressure between 10 ³ and 10 ⁷ Pa, then possibly heated up to the sintering temperature and maintained for a holding time of at least 20 min or in this time of at least 20 min only a slight cooling of maximum 2 ° C / min is carried out and then cooled. When heating up or at the latest when the sintering temperature is reached maintain the set nitrogen atmosphere until at least 1000 ° C is reached in the cooling phase.

Alternatively, a mixture of hard materials and binder metals containing at least 0.2% by mass of nitrogen is pre-pressed and the green compact thus produced is heated to the sintering temperature, the inert gas or vacuum atmosphere set during the heating up, at least temporarily, from reaching a temperature between 1200 ° C. and the sintering temperature is exchanged for this gas pressure atmosphere by admission of nitrogen-containing gases under a pressure of 10 ³ to 10 ⁷ Pa. The sintering time is at least 30 min; when heating from 1200 ° C or later, the nitrogen pressure should be maintained until at least 1000 ° C is reached in the furnace atmosphere when cooling.

However, the above method requires a hard material composition in which, in addition to the toilet and the binder, considerable amounts of further carbides, nitrides or carbonitrides must also be present.

It is an object of the present invention to provide an improved, essentially two-phase hard metal body of the type mentioned at the outset and a method for its production which, compared to the substrate bodies known according to the prior art, provides better adhesion for surface coatings which are deposited from the gas phase , Such layers can e.g. consist of diamond, amorphous carbon, cubic bomitride, carbon nitrides, oxides and metallic hard materials made of carbides, nitrides, carbonitrides and oxicarbonitrides, in particular the elements of the IVa to Vla group of the periodic table.

This object is achieved by the hard metal substrate body according to claim 1, in which, according to the invention, the sum of the binding metals towards the substrate body drops in a depth of 0 to 1 μm to less than half the concentration of the binding metals in the interior of the substrate body. The percentage of dopants in the hard metal, which consists of WC and a binder phase, is according to the invention 4 mass% limited. The percentage of any third cubic phase is also limited to a maximum of 4 vol%.

In contrast to the hard metal bodies created according to the prior art, the aim is not only mere binder depletion in the edge zones near the surface, but rather an edge zone in which the "free spaces" created by binder depletion are "filled" by doping agents. However, the amount of dopants should be limited to 15% by mass, based on the binder metal phase, which in turn can make up 3% by mass to 25% by mass of the total amount. The rest, namely 75 to 97 mass%, consists of the pure toilet hard phase. The concentration of the binder phase in the region close to the surface preferably decreases gradually, whereas the concentration of the dopants, the carbon and the nitrogen gradually increase.

According to a further embodiment of the invention, the grain size of the toilet in the hard metal substrate body is a maximum of 1.5 μm.

The hard metal substrate body described above is particularly suitable for layers of diamond, but also of carbides, nitrides and / or carbonitrides of titanium, zirconium and / or hafnium or of Al ₂ 0 ₃ , HfO ₂ , ZrO ₂ , mixtures of oxides, amorphous Carbon, from cubic boron nitride or carbon nitrides.

Preferably, nitrides of the metallic dopant, e.g. TiN, CrN or VN, enriched.

The method according to claim 6 or claim 7 is used to produce the hard metal substrate body according to the invention.

In the first alternative embodiment, the starting powder mixture of the desired hard metal composition is powder-metallurgically pretreated in a manner known in the prior art, pre-pressed into a green compact and until heated to the sintering temperature, with the vacuum or inert gas atmosphere being replaced by an N ₂ atmosphere with an N ₂ pressure of <10 ⁵ Pa in the heating phase after reaching the eutectic, but at the latest after reaching the sintering temperature, and at least until the sintering temperature is reached or is maintained until the end of the holding time in which the body is kept at the sintering temperature.

As an alternative to this, it is also possible to carry out the nitrogen treatment after the final sintering, specifically by the finished sintered body below the eutectic temperature of an N ₂ atmosphere under a pressure p of 10 ⁵ Pa <p <10 ⁷ Pa for at least 10 min is exposed. This treatment can be carried out either in the cooling phase after sintering or in a second step, possibly also after grinding and / or blasting treatment of the finished sintered body.

The nitrogen atmosphere can be either by introducing nitrogen gas into the furnace atmosphere or by introducing precursors, i.e. N-containing gases, from which nitrogen is formed in situ at the corresponding temperature in the gas atmosphere.

It is generally known that the size of the WC crystallites can be influenced with the time period and with the gas composition at which the sintered body is above eutectic temperatures. Longer treatment times lead to larger WC crystallites.

In a preferred embodiment variant, the body is heated to 1250 ° C. and this temperature is maintained for a period of at least 20 minutes before heating to the sintering temperature is continued. Furthermore, the body is preferably heated in the warm-up phase first in a vacuum and only from approx. 1250 ° C. in an inert gas atmosphere, for example made of argon, to the sintering temperature, when the nitrogen atmosphere is reached at a pressure of at least 10 ⁴ Pa. The heating and cooling rates are preferably at most 10 ° C./min; the corresponding rate is preferably between 2 ° C./min and 5 ° C./min. According to a further embodiment of the invention, up to 15% by mass, based on the binder phase, of carbides, nitrides, carbonitrides of the elements of the Iva, Va and Vla groups of the periodic table or of the AI or complex carbides are additionally complex nitrides in the starting mixture and / or complex carbonitrides of the form T- ₂ AIC, Ti ₂ AIN, Cr ₂ AIN, Cr ₂ AIC, but preferably only in an amount which can be dissolved at most in the binder phase. This solubility limit is determined by the sum of the dissolved elements and can change for each element by adding other detachable elements.

In the above-described treatment of the sintered bodies in a nitrogen atmosphere under a pressure of 10 ² Pa to 10 ⁷ Pa, the dopants or their carbides, nitrides or carbonitrides diffuse in the direction of the substrate surface and displace by enrichment with corresponding hard material particles, which are additionally caused by the combination of the existing nitrogen and at least one of the metals can be strengthened, the binding phase in deeper regions, which impoverishes on the surface. However, nitrogen treatment also affects carbon activity due to the fact that nitrogen is dissolved in the binder phase, which in turn influences the excretion of hard material phases. This can also be used to control hard phase enrichment in the surface.

The invention is explained below using exemplary embodiments.

Show it

1 shows a sintered profile for the treatment of a sample,

2a, b each a semi-quantitative GDOS depth profile of sample A,

3a, b each a semi-quantitative GDOS depth profile of sample C,

Fig. 4 further sintered profiles and 5a, b each show a semi-quantitative GDOS depth profile of sample C which has been subjected to a sintered profile according to FIG. 4.

Five alloys according to the composition listed in the following table were ground, mixed and pressed into a green body in the usual way and then subjected to a sintering treatment, the sintering profile of which can be seen in FIG. 1.

Table 1 Sample composition

Sintered body composition (mass%)

A 92% WC, 7.5 Co, 0.5 Ti ₂ AIC

B 91, 75% WC, 0.75% Cr ₃ C ₂ , 3.75% Co, 3.75% Ni

C 91, 75% WC, 0.75% Cr ₃ C ₂ , 4.5% Co, 1, 5% Ni, 1, 5% Fe

D 91, 75% WC, 0.75% Cr ₃ C ₂ , 7.5% Co

E 91, 4% WC, 0.75% Cr ₃ C ₂ , 0.35% Mo ₂ C, 7.5% Co

The aforementioned alloy A was first heated to 1250 ° C. at a heating rate of 5 ° C./min. This temperature was maintained for about 30 minutes, after which an argon gas atmosphere was set at a pressure of 5 × 10 ³ Pa. At the same time, the heating of the sintered body was continued at a heating rate of 5 ^c C / min, an N ₂ pressure of 7 × 10 ⁴ Pa being set when 1480 ° C. was reached, which pressure was maintained at 1480 ° C. even after the sintering temperature had been reached remained. The sintering time was approximately 1 hour, after which the furnace was switched off.

In the sintered body according to sample A, it was found that the N ₂ treatment affected the regions close to the surface to a depth of up to 1 μm in such a way that the binder phase, ie the sum of the binder metals, became poor and a significant enrichment of the hard material phase on the Surface and in the areas near the surface was generated (see Fig. 2a). This could be both can be determined in the metallographic cross-section as well as purely optically by a color change. 2b shows the ratio of the dopant Ti to the binding metal Co. It can be seen that the doping element in relation to the binding metal accumulates strongly towards the surface of the substrate body and a very thin Ti (C, N) layer is present on the surface.

3a shows a semi-quantitative GDOS depth profile as a further example of the effect of the modification of the edge zone. It can clearly be seen that the sum of the binding metals (Fe, Co, Ni) on the outer surface decreases. 3b shows a ratio Cr / (Co + Fe + Ni) which increases significantly to the surface at lower penetration depths (approx. 0.1 μm). This means that in the binder in the graded edge zone, which is influenced by nitrogen, the Cr content in the binder phase is increased relative to the other elements of the binder phase compared to the inner regions of the alloy which are not influenced by nitrogen. The nitrogen content increases sharply in the peripheral zone, the carbon and tungsten content increases slightly towards the surface.

Samples of the types A to F according to Table 1 were subjected to various annealing and sintering processes under increased nitrogen pressure according to Table 2.

Table 2

Sintered profiles for samples A to F of Table 1

Sample sintered profile

B cycle 7

C cycle 7

A cycle 7

C php_1

A php_1

D php_2

E php_2

C php_2

E php_2

B php_2

D php_2a

F php_2a

D php_2b

F php_2b.

The sintered profiles are shown in Table 3 and Fig. 4.

Table 3

Tabular description of the sintered profiles

Cycle 8

Cycle 7

php_1

Php_2

php_2a

php_2b

A semi-quantitative GDOS depth profile of sample C is shown in FIG. 5, which shows the decrease in the sum of the binding metals in areas near the surface. The sum of the binding metals again shows the same characteristics as in the case of the same vacuum sintered grade. As in the case of alloy C sintered under reduced pressure, the N and the C content are also increased towards the surface. 5b shows a clear increase in the Cr / (Co + Ni + Fe) concentration ratio to zones near the edge.

By choosing the doping elements or their connections and also by choosing the nitrogen pressure, the edge zone of the finished hard metal sintered body can be adjusted in such a way that not only an enrichment of doping agents but also the formation of a diffusion layer from nitrides is promoted. If, for example, Cr or a Cr compound is used as doping, a vacuum sintering with subsequent N ₂ gas phase adjustment at low pressures (<105 Pa) does not result in a chromium nitride layer or enrichment because chromium nitrides do not form at low nitrogen pressures. On the other hand, by doping a V- or Ti-containing phase, the formation of TiN or VN or of Ti (C, N) or V (C, N) can be caused under the same conditions, because vanadium nitrides or carbonitrides already at low nitrogen pressures be formed.

Claims

Expectations

1. Tungsten carbide substrate body, consisting of a WC hard material phase and a 3 to 25 mass% binder phase which, in addition to at least one of the binder metals Fe, Co and / or Ni, also contains up to 15 mass% (based on the binder phase) dopant contains, which consist of the group AI, Cr, V, Nb, Ta, Ti, Zr, Hf, characterized in that the percentage of all dopants in the hard metal is limited to a maximum of 4 mass%, that the proportion of a cubic phase in the hard metal is smaller than 4% by volume and that the binder metal content in a hard metal substrate body edge zone is up to 1 _. μm, preferably up to 0.5 μm, drops to less than 0.5 times the binder content in the interior of the substrate body.

2. Tungsten carbide substrate body according to claim 1, characterized in that the concentration of the binder phase gradually decreases towards the surface of the substrate body and the concentration of the dopant gradually increases in a corresponding manner.

3. Tungsten carbide substrate body according to claim 1 or 2, characterized in that the grain size of the WC is <1, 5 microns, with WC fine grain carbides (grain size <0.8 microns) and / or WC ultra fine grain hard metals (Grain size <0.5 μm) preferably Cr, V and / or Ta are contained as dopants.

4. hard metal substrate body, characterized in that on the substrate body surface at least one layer of a carbide, nitride and / or carbonitride of Ti, Zr and / or Hf and / or Al ₂ 0 ₃ , HfO ₂ , ZrO ₂ , oxides, amorphous carbon, from diamond, cubic bomitride, carbon nitride (CN _X ) or other compounds having at least one of the elements B, C, N and / or O is applied.

5. Hard metal substrate body according to one of claims 1 to 4, characterized in that nitrides or carbo-nitrides of the metallic dopant are enriched in the edge zone near the surface.

6. The method for producing the hard metal substrate body according to one of claims 1 to 5, in which the starting mixture is powder-metallurgically pretreated, pressed into a green body and finally heated and sintered in the atmosphere of a furnace, characterized in that in the heating phase after reaching the Eutectic, but at the latest after reaching the sintering temperature, the vacuum or inert gas atmosphere is replaced by an N ₂ atmosphere with an N ₂ pressure <10 ⁵ Pa and is maintained at least until the sintering temperature is reached.

7. The method for producing the hard metal substrate body according to one of claims 1 to 5, in which the starting mixture is pretreated by powder metallurgy, pressed into a green body and finally heated and sintered in the atmosphere of a furnace, characterized in that after the final sintering or, if appropriate, in a final treatment below the eutectic temperature of the sintered bodies in a ^ atmosphere under one

Pressure (p) of 10 ⁵ Pa <p <10 ⁷ Pa for at least 10 min.

8. The method according to claim 6 or 7, characterized in that the nitrogen atmosphere by introducing precursors, i.e. N-containing gases is set, nitrogen being formed in situ in the gas atmosphere.

9. The method according to any one of claims 6 to 8, characterized in that heated to 1250 ° C during the heating phase and this temperature is held for a period of at least 20 min, preferably more than 1 h, before heating to the sintering temperature is continued.

10. The method according to any one of claims 6, 8 or 9, characterized in that first in the warm-up phase at about 1200 ° C, the previously existing vacuum through an inert gas atmosphere, preferably at a pressure of 10 ³ Pa to 10 ⁴ Pa, and only at When the sintering temperature is reached, the nitrogen-containing atmosphere is set at a higher pressure, preferably> 10 ⁴ Pa.

11. The method according to any one of claims 6 to 10, characterized in that the heating and cooling rate is up to 10 ° C / min, preferably between 2 ° C / min and 5 ° C / min.

12. The method according to any one of claims 6 to 11, characterized in that in the starting mixture up to 15 mass% of the binder phase additional carbides, nitrides, carbonitrides of the elements of the IVa or Vla group of the periodic table or of the AI or complex carbides, complex nitrides and / or complex carbonitrides of the form T- ₂ AIC, Ti ₂ AIN, Cr ₂ AIN, Cr ₂ AIC are contained.